a) Young women with iron deficiency supplemented with 130 mg of elemental iron once a week will have a significantly higher percent absorption when compared with those supplemented with 130 mg daily. b) Young women with iron deficiency will have the same hematologic improvement when treated with 130 mg of elemental iron daily versus with 130 mg of elemental iron weekly. c) Young women with iron deficiency will have the same VO2 max improvement when treated with 130 mg of elemental iron daily versus with 130 mg of elemental iron weekly. A screening process including informed consent, blood work, and history and physical exam will be performed on approximately 125 female long distance runners to yield 25-35 iron deficient individuals. These eligible individuals will be randomized to receive 130 mg of elemental iron either weekly or daily for the next 8 weeks. During those 8 weeks, the study subjects will be asked to keep a 3 day food diary X 2, medication diary, side effect diary, and a training log. They will also undergo a VO2 max study at week 0 and 8. They will undergo the ingestion portion of a stable Fe isotope absorption study at week 0 and 6. They will have additional blood drawn at week 6 (for the results of the first absorption study) and 8 (for the results of the second absorption study and changes from baseline hematologic parameters).